Benchmark-Informed Technical Assessment of an M60 Concrete Matrix with Untreated and Pozzolanic-Slurry-Treated Recycled Coarse Aggregate

Abstract

This technical paper develops a reproducible M60 high-performance concrete programme using untreated and pozzolanic-slurry-treated Recycled Coarse Aggregate (RCA) and evaluates the proposed decision gates against an external benchmark. The nine-mixture matrix comprises a natural-aggregate control (N0), untreated RCA at 25%, 50%, 75%, and 100% replacement (U25–U100), and corresponding treated mixtures (T25–T100). Binder content is fixed at 500 kg/m³ with 10% silica fume, free water is 160 kg/m³, and the water-binder ratio is 0.32. Treatment uses a 70:30 fly-ash solids blend, a 1:1 water-to-solids ratio, 3 min dispersion, and 4 h immersion. Because verified specimen-level results for the proposed N0/U/T matrix are not yet available, published matched natural- and recycled-aggregate self-compacting-concrete data are analyzed only as an external benchmark and are not presented as results of the proposed matrix. Complete fine-plus-coarse aggregate replacement reduced slump flow by 6.1%–9.2%. At 28 days, recycled-to-natural retention was 76.1%–80.3% for compression, 76.4%–80.9% for splitting tensile strength, and 77.9%–82.0% for flexure. Both aggregate families continued to gain strength through 91 days, but the relative gap persisted; the strongest recycled benchmark mixture reached 53.94 MPa at 28 days and 64.97 MPa at 91 days. These findings support a non-compensatory decision rule in which M60 compression, tensile retention, transport durability, carbonation, shrinkage, and chemical resistance must be satisfied before GWP, resource saving, embodied energy, and cost are ranked. The paper provides the experimental matrix, treatment controls, equations, graphs, acceptance gates, and reporting template required for future specimen-level validation.